The present invention relates generally to fuel cells, and more particularly to fuel cells having electrodes with compositional and/or structural gradients.
Fuel cells use an electrochemical energy conversion of a fuel and oxidant into electricity and heat. It is anticipated that fuel cells may be able to replace primary and secondary batteries as a portable power supply. In fuel cells, the fuel (containing a source of hydrogen or other oxidizable compound) is oxidized with a source of oxygen to produce (primarily) water and carbon dioxide. The oxidation reaction at the anode, which liberates electrons, in combination with the reduction reaction at the cathode, which consumes electrons, results in a useful electrical voltage and current through the load.
As such, fuel cells provide a direct current (DC) voltage that may be used to power motors, lights, electrical appliances, etc. A solid oxide fuel cell (SOFC) is one type of fuel cell that may be useful in portable applications, as well as in many other applications.
A significant amount of effort has been expended in optimizing composition and porosity of electrodes. Typical approaches have involved electrodes formed from materials having a constant compositional and structural morphology. More recently, a structural and/or compositional gradient of the electrode in the direction away from the electrolyte appears to provide some benefit in improving performance of SOFC systems. Unfortunately, in both cases, compromises are necessarily made relating to operating temperatures, fuel cell performance, and fuel utilization when using materials with such morphologies.